The fate of former President Barack Obama’s health care initiative, the Affordable Care Act, is once again in jeopardy.The Fifth Circuit Court of Appeals will hear arguments beginning on Tuesday over the latest legal challenge against the landmark legislation, which expands insurance access to millions while mandating every American gets health insurance or pays a tax. A three-panel judge will determine whether the law, also known as Obamacare, was rendered unconstitutional in 2017 when it zeroed out the tax imposed on those who chose not to buy insurance. US District Judge Reed O’Connor, in a ruling in Fort Worth, Texas, declared in December that it did, causing the law’s supporters to appeal.The lawsuit is fully supported by Donald Trump, who on Tuesday tweeted Obamacare would "have been replaced by something far better" if the US Supreme Court had previously deemed it unconstitutional. The result of this challenge could affect protections for people with pre-existing conditions; Medicaid expansions covering roughly 12 million people; and subsidies that help about 10 million others afford health insurance. The case could eventually reach the Supreme Court, where conservative justices have previously rejected the argument that Congress could require everyone to buy insurance under the Constitution’s interstate commerce clause. Opponents to Obamacare have noted the 2012 ruling of a divided Supreme Court that upheld the law.But Chief Justice John Roberts, joining four liberal justices, said Congress did have the power to impose a tax on those without insurance.With no tax penalty now in effect, the Texas lawsuit argues, the individual mandate is unconstitutional and the entire law must fall without it. In addition to the 18 states, two individual taxpayers are part of the lawsuit. The Trump administration is not defending the law and has filed arguments in favour of Mr O’Connor’s ruling.California’s attorney general represents a coalition of mostly Democratic-led states and the District of Columbia seeking to overturn Mr O’Connor’s ruling and uphold the law, along with the US House of Representatives. The law's supporters argue that those who filed suit have no case because they aren’t harmed by a penalty that doesn’t exist; that the reduction of the tax penalty to zero could be read as a suspension of the tax, but the tax’s legal structure still exists; and that, even if the individual mandate is now unconstitutional, that does not affect the rest of the law.Additional reporting by AP